Narrow gauge high strength choked wet tip microwave ablation antenna

ABSTRACT

An electromagnetic surgical ablation probe having a coaxial feedline and cooling chamber is disclosed. The disclosed probe includes a dipole antenna arrangement having a radiating section, a distal tip coupled to a distal end of the radiating section, and a ring-like balun short, or choke, which may control a radiation pattern of the probe. A conductive tube disposed coaxially around the balun short includes at least one fluid conduit which provides coolant, such as dionized water, to a cooling chamber defined within the probe. A radiofrequency transparent catheter forms an outer surface of the probe and may include a lubricious coating.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.12/472,831, filed May 27, 2009, now U.S. Pat. No. 8,292,881, theentirety of which is hereby incorporated by reference herein for allpurposes.

BACKGROUND

1. Technical Field

The present disclosure relates to systems and methods for providingenergy to biological tissue and, more particularly, to a microwaveablation surgical probe having a concentric tubular structure andconical distal tip, and methods of use and manufacture therefor.

2. Background of Related Art

Energy-based tissue treatment is well known in the art. Various types ofenergy (e.g., electrical, ultrasonic, microwave, cryogenic, thermal,laser, etc.) are applied to tissue to achieve a desired result.Microwave energy can be delivered to tissue using an antenna probe.Presently, there are several types of microwave probes in use, e.g.,monopole, dipole, and helical. One type is a monopole antenna probe,which consists of a single, elongated microwave conductor exposed at theend of the probe. The probe is typically surrounded by a dielectricsleeve. The second type of microwave probe commonly used is a dipoleantenna, which consists of a coaxial construction having an innerconductor and an outer conductor with a dielectric junction separating aportion of the inner conductor. The inner conductor may be coupled to aportion corresponding to a first dipole radiating portion, and a portionof the outer conductor may be coupled to a second dipole radiatingportion. The dipole radiating portions may be configured such that oneradiating portion is located proximally of the dielectric junction, andthe other portion is located distally of the dielectric junction. In themonopole and dipole antenna probe, microwave energy generally radiatesperpendicularly from the axis of the conductor.

A typical microwave antenna has a long, thin inner conductor thatextends along the axis of the probe and is surrounded by a dielectricmaterial and is further surrounded by an outer conductor around thedielectric material such that the outer conductor also extends along theaxis of the probe. In another variation of the probe that provides foreffective outward radiation of energy or heating, a portion or portionsof the outer conductor can be selectively removed. This type ofconstruction is typically referred to as a “leaky waveguide” or “leakycoaxial” antenna. Another variation on the microwave probe involveshaving the tip formed in a uniform spiral pattern, such as a helix, toprovide the necessary configuration for effective radiation. Thisvariation can be used to direct energy in a particular direction, e.g.,perpendicular to the axis, in a forward direction (i.e., towards thedistal end of the antenna), or combinations thereof.

Invasive procedures and devices have been developed in which a microwaveantenna probe may be either inserted directly into a point of treatmentvia a normal body orifice or percutaneously inserted. Such invasiveprocedures and devices potentially provide better temperature control ofthe tissue being treated. Because of the small difference between thetemperature required for denaturing malignant cells and the temperatureinjurious to healthy cells, a known heating pattern and predictabletemperature control is important so that heating is confined to thetissue to be treated. For instance, hyperthermia treatment at thethreshold temperature of about 41.5° C. generally has little effect onmost malignant growth of cells. However, at slightly elevatedtemperatures above the approximate range of 43° C. to 45° C., thermaldamage to most types of normal cells is routinely observed. Accordingly,great care must be taken not to exceed these temperatures in healthytissue.

In the case of tissue ablation, a high radio frequency electricalcurrent in the range of about 500 MHz to about 10 GHz is applied to atargeted tissue site to create an ablation volume, which may have aparticular size and shape. Ablation volume is correlated to antennadesign, antenna performance, antenna impedance and tissue impedance. Theparticular type of tissue ablation procedure may dictate a particularablation volume in order to achieve a desired surgical outcome. By wayof example, and without limitation, a spinal ablation procedure may callfor a longer, more narrow ablation volume, whereas in a prostateablation procedure, a more spherical ablation volume may be required.

In some surgical procedures, a microwave antenna probe may be insertedpercutaneously into, for example, a chest wall of a patient. During sucha procedure, negotiating the probe through, for example, fibrousthoracic tissue and ribs may place undue stresses on the probe.Additionally, microwave energy may radiate into the skin, which mayincrease the likelihood of complications, such as skin burn.

SUMMARY

The present disclosure provides an electromagnetic surgical ablationprobe having a cooled and dielectrically buffered antenna assembly. Acable provides electromagnetic energy to the probe via a coaxialconductor and/or provides coolant via a fluid conduit to improve powerdelivery performance and power handling, and to reduce componenttemperatures. Suitable coolants include deionized water, sterile water,or saline.

The probe includes two concentrically-disposed cylindrical tubes. Anouter tube is a catheter formed from a radiofrequency transparentmaterial such as an epoxy glass composite and extends from a proximaldevice handle to a distal tip of the probe. The catheter radiofrequencytransparent material may additionally have a low electricalconductivity, or dielectric properties. In an embodiment, the cathetermaterial may exhibit a low electrical conductivity, or dielectricproperties, at a probe operating frequency (e.g., 915 MHz to 2.45 GHz).An inner tube is formed from conductive material, e.g., a metal such asstainless steel, and extends from the device handle to a proximal end ofthe radiating section. The inner diameter of the outer tube issubstantially equal to the outer diameter of the inner tube.

A metal or plastic tip may be positioned at a distal end of thecatheter. The tip may be made with trocar geometry (e.g., substantiallyconical) to improve ease of insertion of the probe into tissue. The tipand catheter may be coated with non-stick heat shrink material and/orlubricious coating.

An electrical connection is made between the inner metal tube and theouter conductor of the coaxial feedline at a distance of aboutone-quarter wavelength (γ/4) proximally from a distal end of the metalinner tube, forming a short circuited balun. Alternatively, the balunmay be positioned at any odd multiple of one-quarter wavelengths (e.g.,3γ/4, 5γ/4, etc.) from a distal end of the inner metal tube. As usedherein, the term wavelength refers to the wavelength of electromagneticenergy, e.g., microwave ablation energy, corresponding to an operatingfrequency of the disclosed antenna. The circulating coolant, whichpreferably has low conductivity, forms the dielectric insulator of thebalun.

The radiating section of the antenna has a dipole structure. The dipolefeed is constructed by opening (e.g., stripping) the coaxial outerconductor and exposing an extended dielectric and inner conductor of thecoaxial feedline distally. The coaxial dielectric truncation coincideswith the inner conductor increasing in diameter at a cylindricalradiating section that extends further distally toward the distal tip ofthe antenna. The inner conductor may be directly coupled to the tip ofthe antenna. The inner conductor may also flare, spiral or be loadedwith disks to improve radiating performance and provide additionalmechanical strength.

Notches in the balun short permit fluid circulation through the balunstructure into the radiating section for cooling and dielectricbuffering. Screening or mesh may also be used for the balun short. Fluidinflow and outflow control may be accomplished by either using inflowand/or outflow tubes which pass through the short circuit into theradiating section, or by using a extruded low conductivity structure todivide the cylindrical geometry into two sections for inflow andoutflow. The structure may additionally center the coaxial feed line andantenna radiating structure within the catheter tubes.

A microwave ablation antenna according to the present disclosure mayhave advantages, such as quickly achieving a large ablation diameter, anearly spherical ablation shape, low reflected power, cool probe shaft,with a narrower gauge needle size (15 g) for use in percutaneousprocedures. The metal conductive tube may provide increased strength andstiffness, which permits difficult insertion through, for example, thechest wall. The balun short may confine most radiation to the distal tipof the probe, reducing the likelihood of complications from multipleantenna interactions, which may cause skin burn

In one embodiment, an electromagnetic surgical ablation probe accordingto the present disclosure includes a coaxial feedline having an innerconductor, outer conductor and a dielectric disposed therebetween. Theouter conductor is truncated (e.g., stripped), whereby the innerconductor and dielectric extend beyond the outer conductor. A radiatingsection is coupled to the distal end of the inner conductor, and adistal tip is coupled to a distal end of the radiating section. The tipincludes a generally cylindrical proximal tip extension having at leastone o-ring disposed thereabout, which may help seal the coolant chamberfrom fluid leakage. The disclosed probe also includes a ring-like balunshort disposed in electrical communication around the outer conductor,which may help control a radiation pattern of the probe. A conductivetube disposed therethrough. A radiofrequency transparent catheter joinedto a proximal end of the distal tip encloses the probe and defines acoolant chamber within the probe.

Also disclosed is an electromagnetic surgical ablation system whichincludes a source of microwave ablation energy operably coupled to theaforementioned probe by a coaxial feedline.

The present disclosure is also directed to a method of manufacturing amicrowave ablation probe that includes the steps of providing a coaxialfeedline having an inner conductor, an outer conductor, and a dielectricdisposed therebetween. A distal radiating section cylinder is joined toa distal end of the inner conductor and a distal tip is joined to thedistal radiating section cylinder. A balun short having at least onenotch defined therein is positioned on the outer conductor, and at leastone fluid conduit member is positioned on an outer surface of the outerconductor such that the fluid conduit member is longitudinally disposedwithin the notch provided on the balun short. A conductive tube ispositioned around the balun short, and radiofrequency transparentconduit is positioned over the assembly. A distal end of theradiofrequency transparent conduit is fixed to a proximal end of thedistal tip.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 shows a diagram of a microwave ablation system having anelectromagnetic surgical ablation probe in accordance with the presentdisclosure;

FIG. 2 shows a cross sectional view of an embodiment of anelectromagnetic surgical ablation probe in accordance with the presentdisclosure;

FIGS. 3A-3E show perspective views of an embodiment of anelectromagnetic surgical ablation probe at various stages of assembly inaccordance with the present disclosure;

FIGS. 4A-4B show views of another embodiment of an electromagneticsurgical ablation probe at various stages of assembly in accordance withthe present disclosure;

FIGS. 5A-5C show views of yet another embodiment of an electromagneticsurgical ablation probe at various stages of assembly in accordance withthe present disclosure; and

FIG. 6 shows an external perspective view of an embodiment of anelectromagnetic surgical ablation probe in accordance with the presentdisclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure will be describedhereinbelow with reference to the accompanying drawings; however, it isto be understood that the disclosed embodiments are merely exemplary ofthe disclosure, which may be embodied in various forms. Well-knownfunctions or constructions are not described in detail to avoidobscuring the present disclosure in unnecessary detail. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a basis for the claims and asa representative basis for teaching one skilled in the art to variouslyemploy the present disclosure in virtually any appropriately detailedstructure.

In the drawings and in the descriptions that follow, the term“proximal,” as is traditional, shall refer to the end of the instrumentthat is closer to the user, while the term “distal” shall refer to theend that is farther from the user.

FIG. 1 shows an embodiment of a microwave ablation system 10 inaccordance with the present disclosure. The microwave ablation system 10includes an electromagnetic surgical ablation probe 100 connected by acable 15 to connector 16, which may further operably connect the probe100 to a generator assembly 20. Generator assembly may be a source ofablation energy, e.g., microwave or RF energy in the range of about 915MHz to about 2.45 GHz. Cable 15 may additionally or alternativelyprovide a conduit (not explicitly shown) configured to provide coolantfrom a coolant source 18 to the electromagnetic surgical ablation probe100.

In greater detail, and with reference to FIG. 2 and FIGS. 3A-3D, anembodiment of an electromagnetic surgical ablation probe 100 includes ashaft assembly 101 having a coaxial feedline 102 disposed through thelongitudinal axis of the shaft 101. The feedline 102 includes an innerconductor 103 disposed coaxially within an outer conductor 105 and adielectric (e.g., insulator) 104 concentrically disposed between theinner conductor 103 and outer conductor 105. In embodiments, feedline102 has a nominal impedance of about 50 ohms. Inner conductor 103 anddielectric 104 extend beyond outer conductor 105 at a distal end offeedline 102.

A distal radiating section cylinder 124 is coupled to a distal end ofthe inner conductor 103. A distal tip 120 is coupled at a proximal end121 thereof to a proximal tip extension 131. In an embodiment, proximaltip extension 131 and distal tip 120 may be integrally formed. In yetanother embodiment, distal radiating section cylinder 124 may be formedfrom two sections wherein a proximal section is coupled to a distal endof the inner conductor 103, and a distal section is integrally formedwith proximal tip extension 131. Inner conductor 103, distal radiatingsection cylinder 124, proximal tip extension 131 and distal radiatingsection cone 120 may be respectively coupled by any suitable manner ofbonding, including without limitation welding, soldering, crimping, orthreaded fastening. A proximal end of feedline 102 may be operablycoupled to a generator 20 configured to generate microwave ablationenergy in the range of about 800 MHz to about 5 GHz.

In one embodiment, distal tip 120 has a generally conical shape havingan apex at a distal end 122 thereof. However, embodiments are envisionedwherein distal tip 120 may have any shape, including without limitation,a cylindrical, rounded, parabolic, flat, knife-like, and/or flaredshape. Distal tip 120 may be formed from any suitable material, includemetallic, nonmetallic, and polymeric materials.

With reference particularly to FIG. 3D, at least one o-ring 126 ispositioned around distal radiating section cylinder 124 and/or a distalsegment thereof that is integrally formed with distal tip 120. O-ring126 may be formed from any suitable heat-resistant material, and mayadditionally or alternatively be integrally formed with distal radiatingsection cylinder 124 and/or a distal segment thereof that is integrallyformed with distal tip 120. An outer diameter of o-ring 126 isdimensioned to provide a fluid seal with an inner diameter of catheter130 as illustrated in FIGS. 4C and 5B and as will be described ingreater detail below. Distal tip 120 may include at a proximal endthereof a shoulder 123 that has an outer diameter dimensioned to couplewith an inner diameter of conductive tube 116. Additionally oralternatively, shoulder 123 may include an o-ring 126. In oneembodiment, a sealant (not explicitly shown) such as elastomeric polymeror epoxy may be included in a region 125 adjacent to o-ring 126 and/orshoulder 123.

Referring again to FIG. 2, and to FIG. 6, a tubular catheter 130 extendsproximally from a proximal end 121 of distal tip 120. Catheter 130 hasan inner diameter substantially equal to the outer diameter of aconductive tube 116 and of shoulder 123. An outer diameter of catheter130 has an outer diameter that substantially corresponds to that of thebase (e.g., proximal) diameter of distal tip 120. Catheter 130 is formedfrom radiofrequency transparent material. Catheter 130 may be formedfrom material having a low electrical conductivity, or dielectricproperties. In an embodiment, the probe 130 material may have lowelectrical conductivity, or dielectric properties, in a probe operatingfrequency range, e.g., an operating range of about 915 MHz to about 2.45GHz. Catheter 130 may be formed from composite material, such as withoutlimitation, epoxy glass composite, carbon fiber, and the like. In anembodiment, catheter 130 may not be completely transparent toradiofrequency energy, and instead may be nearly or substantiallytransparent. In use, a dielectric constant of catheter 130 may aid inmatching the combined impedance of the probe and tissue in contacttherewith to the impedance of coaxial feedline 102, which in turn mayimprove energy delivery to tissue. Additionally, the low electricalconductivity of catheter 130 may reduce undesired reflection ofradiofrequency and/or microwave energy.

The disclosed probe includes a balun short 110 that is coaxiallydisposed around a outer conductor, located proximally of a distal end119 of outer conductor as best seen in FIG. 3E. Advantageously, balunshort 110 may be positioned a quarter wavelength distance from a distalend 119 of conductive tube 116. Balun short 110 may be formed fromconductive material (e.g., metallic or conductive polymeric material) toform an electrical connection between outer conductor 105 and conductivetube 116. Balun short 110 includes at least one notch 111 definedtherein which may assist in cooling the probe 100 during use. A coolantchamber 117 may be defined by the inner surface of catheter 130, o-ring126, balun short 110, and the outer surface of outer conductor 105.Balun short 110 may additionally or alternatively be formed fromconductive screen, mesh or woven materials. In embodiments, cooling maybe achieved passively by thermal convection (e.g., ventilation providedby the at least one notch 111), or actively by the flow of coolantwithin the probe 100 as will now be described. Catheter 130 and/ordistal tip 120 may include a coating (not explicitly shown), such as alubricious (e.g., non-stick) coating formed from polytetrafluoroethylene(a.k.a. PTFE or Teflon®, manufactured by the E.I. du Pont de Nemours andCo. of Wilmington, Del., USA), polyethylene tephthalate (PET), or thelike. Additionally or alternatively, catheter 130 and/or distal tip 120may include a heat shrink coating, such as polyolefin tubing or anysuitable heat-shrink material.

In an embodiment illustrated in FIGS. 4A and 4B, an inflow tube 140 isdisposed longitudinally along an outer surface of outer conductor 105.Inflow tube 140 includes an open distal end 141 that is configured todeliver coolant fluid to a coolant chamber 117. Inflow tube 140, at aproximal end thereof (not explicitly shown), may be in fluidcommunication with a coolant source 18, such as without limitation acoolant pump or drip bag. Any suitable medium may be used as a coolant.In embodiments, deionized water, sterilized water, or saline may be usedas a coolant. In one aspect, the coolant may have dielectric propertieswhich may provide improved ablation volume and shape, and/or may provideimproved impedance matching between the probe 100 and tissue. Duringuse, coolant flows distally though inflow tube 140 and is introducedinto coolant chamber 117 at the open distal end 141 of inflow tube. Asbest seen in FIG. 4A, inflow tube 140 is positioned within notch 111defined in balun short 110. Balun short 110 includes an outflow notch112 through which coolant may exit coolant chamber 117.

In another embodiment illustrated in FIGS. 5A, 5B, and 5C, a rib 151 islongitudinally disposed between an outer surface of outer conductor 105and conductive tube 116 to concentrically position coaxial feedline 102within conductive tube. Rib 151 is preferably formed from alow-conductivity or insulating material. A second longitudinal rib 151may be included to form an inflow channel 152 and an outflow channel153. The ribs 151 may radially opposed (e.g., offset approximately 180°apart as indexed with reference to the circular cross-section of coaxialfeedline 102 and/or conductive tube 116) and dimensioned to define aninflow channel 152 and outflow channel 153 between conductive tube 116and outer conductor 105 of substantially similar size. Embodiments areenvisioned within the scope of the present disclosure wherein ribs 151are positioned more, or less, than 180° apart. Embodiments having threeor more ribs are contemplated, wherein three or more channels (notexplicitly shown) are formed. The additional channels may be used tocirculate different types of coolant, having, for example, differingdielectric and/or thermal properties. Additionally, the channels maydeliver to the probe, and/or to tissue, medicaments, bioadhesives,radioisotopes, and/or other useful therapeutic compounds. Withparticular reference to FIG. 5A, the present embodiment includes a balunshort 113 having rib notches 115 that are adapted to position and retainribs 151. Balun short 113 additionally includes coolant notches 114 thatare adapted to facilitate the flow of coolant past balun short 113, aswill be readily appreciated. In embodiments, balun short 113 may beconstructed from perforated metal, metal mesh, or screen material.

A method of manufacturing a high-strength microwave ablation probe 100is shown in accordance with the present disclosure with reference now toFIGS. 3A-3E. It is to be understood that the steps of the methodprovided herein may be performed in combination and in a different orderthan presented herein without departing from the scope and spirit of thepresent disclosure.

With reference to FIG. 3A, a coaxial feedline 102 is provided having aninner conductor 103, a dielectric 104 and an outer conductor 105. Asshown in FIG. 3B, the inner conductor 103 and dielectric 104 is extendedbeyond outer conductor 105 at a distal end thereof. In one embodiment ofthe disclosed method, a stripping tool may be used to trim a distalportion of outer conductor 105 to expose inner conductor 103 anddielectric 104. As seen in FIG. 3C, a distal radiating section cylinder124 is provided and affixed to inner conductor 103 by any suitablemanner of attachment, for example and without limitation, by laserwelding. As shown in FIG. 3D, a distal tip 120 is provided, having agenerally conical shape and including a proximal tip extension 131 thatis dimensioned to couple to a distal surface 129 of distal radiatingsection cylinder 124. Distal tip 120 is affixed to distal radiatingsection cylinder 124 by any suitable manner of bonding, such as withoutlimitation, by laser welding or threaded fastener. At least one o-ring126 is positioned on proximal tip extension 131. In a step illustratedin FIG. 3E, a balun short 110 having a notch 111 defined therein ispositioned and electrically coupled to outer conductor 105.

In an embodiment best illustrated in FIG. 4A, an inflow tube 140 islongitudinally disposed along outer conductor 105 and positioned withinnotch 111. As seen in FIG. 4B, a conductive tube 116 is positioned overthe assembly 139. A distal end 119 of conductive tube 116 is positioneddistally of balun short 110 at a distance of about one-quarterwavelength therefrom. In a step depicted in FIG. 6, catheter 130 ispositioned over the assembly 139 and joined to a proximal end 121 of tip120. An inner diameter of catheter 130 may be dimensioned to engage anouter diameter of shoulder 123. Additionally or alternatively, a sealant(not explicitly shown) may be applied to region 125 adjacent to o-ring126 and/or shoulder 123.

In an embodiment best illustrated in FIG. 5A, a balun short 113 havingtwo pairs of radially opposed notches 114, 115 defined therein ispositioned and electrically coupled to outer conductor 105. A pair ofribs 151 are longitudinally positioned within a respective notch 115. Adistal end 119 of conductive tube 116 is positioned distally of balunshort 110 at a distance of about one-quarter wavelength therefrom. In astep depicted in FIG. 6, catheter 130 is positioned over the assemblyand joined to a proximal end 121 of tip 120. An inner diameter ofcatheter 130 may be dimensioned to engage an outer diameter of shoulder123. Additionally or alternatively, a sealant (not explicitly shown) maybe applied to region 125 adjacent to o-ring 126 and/or shoulder 123.

The described embodiments of the present disclosure are intended to beillustrative rather than restrictive, and are not intended to representevery embodiment of the present disclosure. Further variations of theabove-disclosed embodiments and other features and functions, oralternatives thereof, may be made or desirably combined into many otherdifferent systems or applications without departing from the spirit orscope of the disclosure as set forth in the following claims bothliterally and in equivalents recognized in law.

What is claimed is:
 1. An ablation probe, comprising: a coaxial feedlinehaving an inner conductor, an outer conductor disposed coaxially aboutthe inner conductor, and a dielectric disposed therebetween, wherein theinner conductor and dielectric extend beyond the outer conductor at adistal end thereof; a balun short disposed in electrical communicationaround the outer conductor and including a first longitudinal notch andat least one second longitudinal notch defined therein; a conductivetube disposed coaxially around the balun short; and at least one fluidconduit defined longitudinally within the conductive tube, the fluidconduit including an inflow tube disposed longitudinally along the outerconductor and positioned at least partially within the first notch. 2.The ablation probe in accordance with claim 1, wherein the balun shortincludes at least two first notches defined therein adapted to receive acorresponding number of rib members and includes at least two secondnotches defined radially therebetween, wherein the at least two ribmembers are disposed longitudinally along the outer conductor andpositioned at least partially within the respective notches thereof todefine at least two fluid conduits within the conductive tube.
 3. Theablation probe in accordance with claim 1, wherein a distal end of theconductive tube is positioned about one quarter wavelength distally fromthe balun short.
 4. The ablation probe in accordance with claim 1,wherein the balun short is formed from material selected from the groupconsisting of conductive screen material, conductive mesh material, andconductive woven material.
 5. The ablation probe in accordance withclaim 1, wherein the balun short is formed from material selected fromthe group consisting of conductive metallic material and conductivepolymeric material.
 6. The ablation probe in accordance with claim 1,further comprising a radiating section having a proximal end operablycoupled to a distal end of the inner conductor.
 7. The ablation probe inaccordance with claim 6, further comprising a distal tip coupled to adistal end of the radiating section, wherein the distal tip includes agenerally cylindrical proximal tip extension having at least one o-ringdisposed thereabout.
 8. The ablation probe in accordance with claim 7,further comprising a catheter coaxially disposed around the conductivetube, wherein a distal end of the catheter is joined to a proximal endof the distal tip to define a coolant chamber therein.
 9. An ablationsystem, comprising: a source of microwave ablation energy; a coaxialfeedline operatively coupled to the source of microwave ablation energy,wherein the coaxial feedline includes an inner conductor, an outerconductor disposed coaxially about the inner conductor, and a dielectricdisposed therebetween, wherein the inner conductor and dielectric extendbeyond the outer conductor at a distal end thereof; a balun shortdisposed in electrical communication around the outer conductor andincluding a first longitudinal notch and at least one second notchdefined therein; a conductive tube defined coaxially around the balunshort; and at least one fluid conduit defined longitudinally within theconductive tube, the fluid conduit including an inflow tube disposedlongitudinally along the outer conductor and positioned at leastpartially within the first notch.
 10. The ablation system in accordancewith claim 9, further comprising a source of coolant in fluidcommunication with the at least one fluid conduit.
 11. The ablationsystem in accordance with claim 9, wherein the balun short includes atleast two first notches defined therein and at least two second notchesdefined radially therebetween; and at least two rib members disposedlongitudinally along the outer conductor, wherein each rib member ispositioned at least partially within a first notch to define at leasttwo fluid conduits within the conductive tube.
 12. The ablation systemin accordance with claim 9, wherein a distal end of the conductive tubeis positioned about one quarter wavelength distally from the balunshort.
 13. The ablation system in accordance with claim 9, wherein thebalun short is formed from material selected from the group consistingof conductive screen material, conductive mesh material, and conductivewoven material.
 14. The ablation system in accordance with claim 9,wherein the balun short is formed from material selected from the groupconsisting of conductive metallic material and conductive polymericmaterial.
 15. The ablation system in accordance with claim 9, furthercomprising a radiating section having a proximal end operably coupled toa distal end of the inner conductor.
 16. The ablation system inaccordance with claim 15, further comprising a distal tip coupled to adistal end of the radiating section, wherein the distal tip includes agenerally cylindrical proximal tip extension having at least one o-ringdisposed thereabout.
 17. The ablation system in accordance with claim16, further comprising a catheter coaxially disposed around theconductive tube, wherein a distal end of the catheter is joined to aproximal end of the distal tip to define a coolant chamber therein. 18.The ablation system in accordance with claim 9, wherein the catheter isformed from radiofrequency transparent material having an electricalproperty selected from the group consisting of a low electricalconductivity and a dielectric.
 19. The ablation system in accordancewith claim 9, wherein a distal end of the inflow tube is in fluidcommunication with the coolant chamber.
 20. A method of manufacturing anablation probe, comprising the steps of: providing a coaxial feedlinehaving an inner conductor, an outer conductor, and a dielectric disposedtherebetween; positioning a balun short on the outer conductor; forminga notch defined longitudinally in the balun short; positioning at leastone fluid conduit member on an outer surface of the outer conductor,wherein the conduit member is longitudinally disposed within the notch;positioning a conductive tube around the balun short.